How was the first curd formed?

The first curd likely formed through the natural process of milk fermentation, where bacteria present in the environment or on the milk itself converted lactose into lactic acid. This acidification caused the proteins in the milk, particularly casein, to coagulate and thicken, resulting in curds. Early humans may have discovered this process accidentally, noticing that milk left out could transform into a thicker substance. Over time, this led to the intentional production of curd and cheese.